The Green Bay Packers are 3-0 and over the past two weeks they’ve vanquished a couple of teams with whom they had some unhappy recent history.

In Week 2, the Packers beat the Seattle Seahawks, they of the notorious 2012 Fail Mary and painful 2014 NFC Championship Game losses. Last week, Green Bay triumphed at home over the Kansas City Chiefs, the team that handed the Packers their first and only regular-season loss the last time they started a season 3-0, back in 2011, when they went 13-0 and finished 15-1.

And now, it’s the San Francisco 49ers, who have defeated the Packers the last four times they’ve met, including in season-ending playoff games in 2012 and 2013. So, the quest for vengeance continues this week.

Aaron Rodgers, with the NFL’s best passer rating, and the Packers’ machinelike offense will be facing a far more toothless defense than the one that held them to an average of 25.3 points in the previous four matchups. This year’s Green Bay attack is averaging nearly a touchdown more than that (32.0 points per game), good for fourth in the NFL, while San Francisco’s defense is second-last in points allowed (31.0).

It’s no better on offense for the 49ers, who are the league’s worst-scoring offense, averaging just 15 points a game. The Packers’ suddenly fierce defense, led by Clay Matthews, is tied for third in sacks, with 11, and is surely looking to make life miserable for quarterback Colin Kaepernick, who has terrorized Green Bay with his arm and legs in the past.

Let’s take a closer look at this Sunday’s showdown in San Francisco, in which the Packers are favored by 8.5 points.

3 things to watch:

— The right side of the 49ers’ offensive line. It’s not good. The line has given up eight sacks overall, which isn’t horrible, but right guard Jordan Devey and tackle Erik Pears are not starting-caliber players. In Week 2, the Steelers had five sacks, and it could be a similar story against Green Bay’s pass rush. The Packers surely remember how Kaepernick and the 49ers have abused them in recent years, and the defense will want revenge. Linebacker Julius Peppers, defensive end Mike Daniels and Matthews have seven sacks between them; more should come on Sunday.

— 49ers wide receiver Torrey Smith. Presumably, Packers defenders will be watching the speedy wideout, and hopefully they are watching him from the front and not seeing the back of his No. 82 streaking past them toward the end zone. Smith is really the only game-breaker San Francisco has, and while he only has seven receptions for 131 yards through three games, one of those catches was a 75-yard touchdown. The free-agent signee was tied for sixth in the NFL in catches of at least 20 yards in 2013, with 20, and at 26 years old he still runs very well. He’ll likely be matched up against Packers top corner Sam Shields, who has the speed to stay with Smith and snagged his first interception last week.

— Packers young receivers. Last week, rookie Ty Montgomery scored his first career touchdown. He’s caught all six passes thrown to him for 51 yards this season and seems quickly to be earning Rodgers’ trust. The third-rounder has shown his dynamic ability as a returner and seems on the verge of breaking out for a huge play on offense very soon. Alternatively, second-year wideout Jeff Janis, who has prototypical size and speed, has shown he’s still raw in his routes; targeted just once, Janis doesn’t yet have Rodgers’ confidence. With Davante Adams (ankle) unlikely to play Sunday — and Jordy Nelson out for the season, of course — the Packers, who use three-receiver sets almost all the time, need their young pass-catchers to step up and complement veterans Randall Cobb and James Jones.

2 things to remember:

— Kaepernick has killed the Packers in the past. He’s having an awful start to this season — a 71.1 passer rating and four interceptions to two touchdowns in three games — and perhaps his true limitations are now showing with a much weaker supporting cast. But let’s not forget that Kaepernick’s natural gifts of a big arm and fast legs have had plenty of success exploiting the Packers’ past defensive weaknesses of yielding the deep ball and not containing mobile quarterbacks. Kaepernick has a 3-0 record against Green Bay with a passer rating of 101.3 and 318 rushing yards. This week, Matthews, an outside-turned-inside linebacker who essentially is just a free defender who gets to play on instinct, might spy Kaepernick. And surely, No. 52 will look for any chance he gets to lay a big hit on him.

— Rodgers is not playing at home. Nor against the Bears. Over the past few weeks, the echo chamber of Rodgers adoration has become even more amplified than usual. Indeed, the defending MVP has played remarkably: a league-best 135.4 passer rating, 10 touchdowns and zero interceptions. In fact, you might have heard something about his interceptions — how he hasn’t thrown one at home since, like, the 1950s. Well, Rodgers is not playing at Lambeau Field this week; nor is he playing the Bears, his Week 1 opponent, against whom he has his best career numbers. He’s playing on the road at San Francisco, a team whose defense has kept him to a 97.1 passer rating — still very good but almost 10 points less than his career mark of 106.8. Will any of that matter, though?

1 key matchup:

Packers run defense vs. 49ers rushing offense

We could also call this Dom Capers vs. The Option, because the Packers’ defensive coordinator has thus far been flummoxed by the 49ers’ college-inspired attack. In the 2012 playoffs, Kaepernick ran the ball 16 times for 181 yards (11.3 average), while former running back Frank Gore carried 23 times for 119 yards (5.2) on a 323-yard rushing day. In the 2013, playoffs, Kaepernick ran seven times for 98 yards (14.0). This year, though, the dynamics are much different. Gore is gone and Kaepernick has rushed 23 times for 138 yards (6.0), while the Packers’ run defense has been much improved. Green Bay allowed just 90 combined rushing yards the past two weeks to Seattle’s Marshawn Lynch and Kansas City’s Jamaal Charles, two of the league’s best backs. Still, the run defense is ranked 27th and has given up a total of 383 yards in three games, largely because of a big day in Week 1 by Chicago’s Matt Forte. Similarly, the 49ers running game has also been inconsistent. In the season opener, Carlos Hyde carried 26 times for 168 yards (6.5) and two touchdowns. In the next two games, though, he rushed for a combined 94 yards on 28 carries (3.4). So, on the ground on both sides, it’s been a bit of Jekyll and Hyde; which one will prevail on Sunday will go a long way to determining the winner.